This invention relates to an anisotropic magnet and, more particularly, to improvement of a surface magnetic field after magnetization, and further relates to a magnet capable of various uses requiring a strong surface magnetic field or a deep magnetic induction line permeation or "reach."
Magnets in accordance with the present invention can be widely used, for example, as magnets for signals, for axial gap motors, for magnetrons, for length measuring machines, for small precision motors, for fixing paper or sheets, and for health improving appliances. They can accordingly be variously shaped.
Conventionally sintered magnets such as rare earth magnets and ferrite magnets or plastic magnets have been used for such purposes. In any of these conventional magnets, magnetic powder particles are oriented in the direction of thickness as shown in FIG. 11(a) of the drawings. Accordingly, the magnetic characteristics of the magnet are determined by the kinds of raw material used in making it, and by the particular content of the magnetic powder.
An anisotropic magnet improved in magnetic characteristics by orienting the magnetic powder particles, is disclosed in Japanese Patent Publication No. 63-59243. In this magnet, as shown in FIG. 12(b) of this specification, the axes of easy magnetization of the particles are convergently oriented from the non-application faces of the magnet (all faces other than the face of application) toward the face of application of the magnet. By applying this orientation the magnetic flux density per unit area (or the magnetic fluxes per unit line) can be increased.
However, it is necessary for a ring-shaped magnet, used for example for a signal which detects magnetic fluxes with a so-called Hall device, to have a high surface magnetic field peak value. Conventional techniques have been unable to accomplish this. In the case of a magnet for use in a length measuring machine, or in a small precision motor, it is necessary to further improve the surface magnetic field of the magnet to improve its accuracy.
There is also a need to provide such improved magnets at a comparatively low price. It is further important to provide a ferrite sintered magnet or a plastic magnet having a high surface magnetic field.